The present invention relates to a ball joint, and more particularly, to a ball joint preferably used to connect a distal end of a support strut to a door, which operates to keep opening of a door, such as a back door of a hatchback vehicle or a mini-van, or a trunk door of a general automobile, such as a sedan.
In a back door of an automobile, such as a hatchback or a mini-van, or a trunk door of a general automobile, such as a sedan, as shown in FIG. 11, support struts b for keeping a door a (in FIG. 11, a back door of a hatchback is shown) open in opening the door a are attached. In this case, since a connecting part between a distal end of the strut bar d of the support strut b and the door a is subjected to a very complicated movement by opening and closing operations of the door a, in order to sufficiently correspond to the complicated movement, a ball joint c is generally used for connecting the strut bar d with the door a.
Conventionally, as the ball joint c, a ball joint as shown in FIG. 12 has been proposed (Japanese Patent Publication (KOKAI) No. 6-272710). Namely, in this ball joint, as shown in FIG. 12, a joint device f having a substantially cylindrical ball holder e is attached to a distal end of a strut bar d, and a spherical fitting part h of a ball stud g attached to the door a is inserted into an elastically deformable C-shaped fitting ring j disposed in the ball holder e of the joint device f. Then, an upper surface of the ball holder e is closed by a cap i.
In the joint device f, as shown in FIGS. 13(a)-13(c), three ball abutting ribs k, k, k' are formed along an axis of the ball holder e to project from an inner peripheral surface of the ball holder e, and a ring-shaped projecting stand m is projected along a periphery of a lower end of the inner peripheral surface. The fitting ring j is provided between the projecting stand m and the ball abutting ribs k, and the ball abutting rib k' is disposed in a slit n of the fitting ring j to thereby prevent the fitting ring j from rotating. And, the spherical fitting part h of the ball stud g is pressed into the ball holder e from an opening at a lower end thereof.
When the fitting part h is inserted, the fitting ring j once expands, so that the spherical fitting part h is fitted between the fitting ring j and the ball abutting ribs k, k, k' to thereby attach the ball stud g to the joint device f. In this case, an upper surface of the spherical fitting part h abuts against the ball abutting ribs k, k, k' and is supported, and a lower side surface thereof is supported by the fitting ring j, which is elastically returned to the original state by shrinking the expanded diameter. Accordingly, the spherical fitting part h can be surely fitted into the ball holder e of the joint device f.
In the conventional ball joint, however, when the spherical fitting part h of the ball stud g is pressed into the ball holder e, the fitting ring j sometimes moves or escapes upwardly, so that the ball stud g may not be attached to the joint device f.
Namely, since the ball abutting rib k' in the ball abutting ribs k, k, k' is located in the slit n of the C-shaped fitting ring j, when the spherical fitting part h of the ball stud g is pressed into the ball holder e of the joint device f, the ball abutting rib k' does not operate to hold the fitting ring j. The ring j is held by the other ball abutting ribs k to thereby be prevented from escaping or moving upwardly. In this case, as shown in FIG. 13(c), since the fitting ring j may become obliquely such that the side of the ball abutting rib k' is lifted upwardly, the fitting part h of the ball stud g may not be inserted inside the fitting ring j. In some cases, the fitting ring j may be pushed out from the ball holder e.
In this case, as shown in FIG. 12, since the cap i is mounted by inserting a cylindrical leg o projecting from a lower surface thereof into the ball holder e, if the fitting part h of the ball stud g is inserted after the cap i is mounted, the fitting ring j is pressed by the leg o to thereby prevent the aforementioned problem. In the structure of the conventional ball joint, therefore, the fitting part h of the ball stud g must be pressed into the cap only after the cap is mounted, so that a process of work is limited. Therefore, as in an embodiment of the invention described later, in case the distal end of the strut bar d is engaged with a fitting convex provided at the cap to thereby fix and couple the strut bar d with the joint device, when the joint device is fixed and coupled with the strut bar d after the fitting part h of the ball stud g is inserted into the joint device, the conventional structure of the ball joint can not be adopted.
In view of the foregoing, an object of the present invention is to provide a ball joint in which, even before the cap is mounted, the spherical fitting part of the ball stud can be successfully inserted into the joint device with good workability while escape of the fitting ring can be prevented.